Because the zeolite Y is a solid acid having acidity, the zeolite Y is used as solid acid catalyst in hydrotreating or in hydrocracking hydrocarbon oils. Especially in the hydrotreating of heavy hydrocarbon oils, ultra-stable zeolite Y (USY) having been subjected to de-aluminum processing is advantageously used. The USY has a unit cell dimension smaller than that of synthetic zeolite Y and also has a high SiO2/Al2O3 molar ratio, and therefore the USY has high heat resistance. In addition, as for pore distribution, pore volume of pores in the range from 20 to 600 Å (mesopore volume) is larger than that of the synthetic zeolite Y.
The acidic characteristic of the zeolite Y varies according to the SiO2/Al2O3 molar ratio, and since the ultra-stable zeolite Y (USY) having been subjected to de-aluminum processing has a high SiO2/Al2O3 molar ratio, therefore the acidity of solid acid is strong, but the acid amount is small. Preferably the zeolite Y used for hydrotreating of hydrocarbon oils is required to have a large mesopore volume and a large amount of solid acid.
Japanese Patent Laid-Open Publication No. HEI 9-255326 (Patent document 1) discloses faujasite-type zeolite having two types of pores, homogeneous micropores and homogeneous mesopores and a method of producing the zeolite. The document describes that the zeolite has the mesopores suited to cracking of residual oils in addition to the micropores, and can advantageously be used for catalytically cracking residual oils. When the zeolite is used for hydrotreating of hydrocarbons, the effect of dispersing heavier hydrocarbons is not sufficient because pore volume of pores having the diameter larger than 50 Å is small, and therefore the further improvement has been desired.
Japanese Patent Laid-Open Publication No. 2002-255537 (Patent document 2) discloses novel zeolite having a large number of mesopores and providing excellent solid acid catalyst. The novel zeolite has the aluminum-silicon atomic ratio (Al/Si) in the range from 0.01 to 0.2, and volume percentage of mesopore volume of pores having the particle diameters in the range from 50 to 1000 Å in the range from 30 to 50%. Furthermore, in the zeolite, the mesopore volume is 0.14 cc/g or more, and a percentage of 4-coordinate aluminum atoms against the total aluminum atoms is 25% or more, which indicates that the zeolite has a large mesopore volume.
Patent document 2 discloses a method of producing novel zeolite including a step of immersing ultra-stable zeolite Y (USY) having a large mesopore volume as a feed material in an aqueous solution of sodium aluminate for reaction to insert aluminum atoms into the zeolite frame, and the conditions for reaction include a concentration of aluminum in the aqueous solution in the range from 0.03 to 0.1 mole/l, pH of the aqueous solution in the range from 11 to 12, the reaction temperature in the range from 10 to 40° C., and the reaction time in the range from 1 to 200 hours.
In the method, however, there is the problem that, because the feed USY is treated with an alkaline aqueous solution with the pH in the range from 11 to 12, crystallinity of the obtained zeolite is low. Because of the problem, when the zeolite is used for hydrotreating of hydrocarbons, an amount of a solid acid as a catalytically active point in the zeolite is small, and high cracking capability can not be obtained disadvantageously.
Japanese Patent Publication No. 3341011 (patent document 3) discloses a catalyst carrier made from zeolite in which ultra-fine particles of an oxide of a metal belonging to the titanium group are introduced in the mesopores for forming a complex and an atomic ratio of aluminum and silicon included in the zeolite (Al/Si) is in the range from 0.01 to 0.1, and catalyst in which a metal having the hydrogenating capability is carried on the catalyst carrier. Patent document 3 also discloses a method of preparing the catalyst carrier, and the method uses zeolite having mesopores as a feed material and includes the steps of contacting an aqueous solution of salt of titanium group to the zeolite at the pH of 0.8 to 2, washing the zeolite with water, drying the zeolite and then sintering the zeolite at a temperature in the range from 400 to 600° C.
In the catalyst carrier, however, ultra-fine particles of metallic oxide of the titanium group with a diameter in the range from 5 to 10 nm are present on inner surface of the mesopores of the zeolite, and furthermore 6-coordinate aluminum removed from the frame structure is present in the zeolite. Because of the features as described above, when the zeolite is used for hydrotreating of hydrocarbons, the heavy hydrocarbons are not sufficiently cracked, and the selectivity for middle fractions is disadvantageously low, and there is the need for overcoming the problems as described above.